1. Field of the Invention
The present invention relates to the measurement of the viscoelasticity of saliva, and more particularly, to a device for the measurement of saliva viscoelasticity in order to determine a woman's ovulation time.
2. The Prior Art
It has been known that the cervical mucus of a female has a maximum fluidity just before ovulation, where ovulation is defined as the moment that an ovum is released from the follicle. This knowledge lead to the applicant's previous activities in the development of techniques for monitoring the viscoelasticity, or tackiness, and other properties of cervical mucus as a predictor of time of ovulation and to improvements in rheometer or viscometer apparatus for measuring such viscoelastic properties. See, for example, L. E. Kopita and H. J. Kosasky, "The Tackiness Rheometer Determination of the Viscoelasticity of Cervical Mucus," Human Ovulation, edited by E. S. E. Hafez, Elsevier, North-Holland Biomedical Press, 1979, pp. 351 et seq., and U.S. Pat. Nos. 4,002,056 and 4,167,110. Though the viscoelasticity of the cervical mucus has several small dips in its characteristic curve of viscosity versus time preceding, during, and following ovulation (a four-day period), there is a distinct identifiable minimum viscoelasticity. Instruments designed to measure this effect are described in, for example, U.S. Pat. Nos. 4,002,056 and 4,072,045.
Saliva is now known to undergo chemical changes during the menstrual cycle, including a change in its viscoelasticity. Especially pronounced is the change in viscoelasticity of sublingual saliva, the saliva found under the tongue. See, for example, S. S. Davis, "Saliva is Viscoelastic", Experientia, 26:1298, (1970), and R. H. Davis et al., "Saliva Viscosity Reflects the Time of Ovulation", Experientia, 30:911, (1974). As described in U.S. Pat. No. 4,779,627, issued on Oct. 25, 1988 to the present applicant, and entitled PROCESS AND APPARATUS FOR DETERMINING FEMALE OVULATION TIME BY MEASUREMENT OF SALIVA VISCOELASTICITY, incorporated herein by reference, the applicant previously discovered that sublingual saliva has a unique and reliably measurable minimum in viscoelasticity that is coincident with the ovulation cycle and its surge of estradiol.
There are devices on the market for measuring viscoelasticity to determine ovulation time, but these devices are designed to use cervical mucus as a sample medium, rather than saliva. The viscoelasticity of cervical mucus is an order of magnitude higher than that of saliva. So, devices designed to use cervical mucus as a sample medium are typically not sensitive enough to use saliva as a sample.
The above-identified U.S. Pat. No. 4,779,627, in addition to disclosing a process for determining female ovulation time by measuring saliva viscoelasticity, discloses a device for measuring the viscoelasticity of the sublingual saliva. The device has a shape somewhat like a syringe, with an outer cup, an inner cup concentric with and located within the outer cup, and a plunger. A roughened surface on the end of the plunger holds the saliva sample. The plunger is inserted into the inner cup until the saliva sample is compressed against the bottom of the inner cup. A predetermined amount of weight pulls the inner cup downward, stretching the saliva sample. If the viscoelasticity of the saliva is low, the saliva sample will fracture, causing the inner cup to fall to the bottom of the outer cup. An indicator at the bottom of the outer cup indicates that the inner cup has fallen to the bottom which, in turn, indicates that ovulation will soon take place. If, however, the viscoelasticity of the saliva is high, the saliva sample will hold the plunger and inner cup together so that the inner cup will not fall to the bottom, indicating that ovulation will not take place in the near future.
This device has several disadvantages. One is that the device can only be used conveniently for one person. The amount of weight that pulls the inner cup downward is selected for a specific person. There must have been a sublingual saliva sample measured from the same person at a time when the sublingual saliva is know to have the minimum viscoelasticity in order to select the amount of weight.
A second disadvantage is that the device must be taken apart in order to take a sample. The plunger must be removed from the inner cup before being inserted in the mouth to obtain a saliva sample. This has the potential for the person to easily contaminate the saliva sample by incorrectly reinserting the plunger after taking the sample, invalidating the measurement.
Thus, there continues to be a need for a device for measuring the viscoelasticity of saliva to determine a female's ovulation time that is easy to use, does not have to be calibrated for an individual, and has a low chance of sample contamination.